As I said in the last part, there are a lot of benefits to linear design. You can control the pace at which the player is introduced to new content and harder challenges. What if we want the feeling of exploring a non-linear space, while also creating a sort of linear-experience of introducing challenges to the player?

This is where the concept of gating mechanics comes in to create implicit linearity. You can gate off certain areas of a space until the player completes a certain challenge, and thus, to varying degrees, control the order in which the player does things. This has the added bonus of making the player have to figure out the underlying order of actions they need to perform to get through an area.

The classic example of this is the key mechanic in Legend of Zelda dungeons. One path is blocked off, requiring the player to find a different path which contains a challenge where reaching the goal reward the player with a key, which then lets them return to the original locked door and progress. Thus you end up with a mostly linear order in which the player must progress through the dungeon, while still giving them the freedom to explore the space that is currently open to them.

This can extend to the structure of a whole game. The so-called “Metroidvania” structure is built around limiting your progression through an otherwise open world by making areas blocked off until you acquire a certain item or skill, and thus forcing the player to complete the areas of a game in a specific order. You need skill 1 to access the area containing skill 2, which you need to access the area containing skill 3 and so on.

An important quality of this is that once the player has all the keys, or has all the skills, they can then move freely through the space that they’ve unlocked. As a designer, you can then reward this by, for example, putting an optional bonus item in area 1 that can only be reached by going back once you’ve gotten skill 3.

And, as with anything, this implied linearity is a matter of degrees. Within the scope of the structure you’ve defined, you can have pockets choice. You can have a few challenges the player can complete in any order, optional challenges, and side-areas that reward exploration.

Here are a few examples. In the first example, you are given 4 paths you can choose from at the start. Three of them contain gems, one contains the gun (which you don’t have at the beginning). You must get the three gems to reach the goal, and you’ll probably want to get the gun, as it’ll be very useful, but it isn’t required.

In this second example, blocks have been placed making it so you must go through the challenges in a specific order. Also of note in this example is that I’ve added an example of a “metroidvania” style mechanic. The path to the right which leads to the right-most and upwards challenge can’t be reached without a gun to destroy the blocks. Before you can get the gun, you have to get the first gem in the downwards path.

In the third example, I’ve set it up so that you have some choice in the order you can face the challenges, but there are still some things which determine the order. You must get the gun before being able to reach the upwards path, and you need to do all the other challenges before you can reach the right-most path, but you could do the upwards path before the downwards path or vice-versa, and the same goes for the left path and the downwards path.

Another thing to notice in those examples is how I set up the gating. Remember that the point of this is to take advantage of the pacing that we’re able to create with linear levels. In the second example, you start by going through two challenges that each introduce one enemy type. The next two challenges then combine those enemy types. In the third example, you will at the very least be introduced to the triangle enemies on their own before seeing them combined with the shooter enemies, and thus won’t be introduced to two enemies at once.

This is a powerful tool to control how the player experiences your level, while still giving them some level of freedom. Even in the second example, despite the fact that you are completing the challenges in a set order, it feels more open than it would if you had put the challenges one after another in a straight line. The player explores what area of the game-space they’ve been given access to, sees the areas that are blocked off, then finds a way to open up those areas.

Next time I want to talk about how the player goes about navigating through these sorts of open and non-linear spaces, and how you as the designer can help guide them without them feeling like they’re being dragged by the hand.